Personal care compositions such as face-washes, body-washes, hand-washes and shampoos etc. are made to look aesthetically attractive by incorporation of the pearlescent additives. These pearlescent additives impart iridescent sheen or glow to personal and home care formulations. The examples of commonly used pearlescent additives are monoesters or diesters of ethylene glycol (Formula I), propylene glycol, oligomeric alkylene glycols, glycerol esters of fatty acids, typically higher carbon chains with C14 to C22 and monoalkanol amides of fatty acids (Formula II);
in which R1 denotes C13 to C21 alkyl group, R2 is H or R1CO and R3 is C8 to C22 alkyl group.
A typical procedure for converting the dull appearance of cosmetic formulations (face-wash, body-wash, shampoo and other aqueous compositions of surfactants) into a pearly (shiny) look involves addition of pearlescent additive (pearly wax) like distearate of ethylene glycol to the entire formulation and heating under agitation above the melting points of the pearlescent additives (70-80° C.) to ensure homogeneous mixture. This is then followed by cooling the entire mass gradually under slow agitation. This way, the pearly waxes are allowed to crystallize into platelet like structures so that the uniformly dispersed platelets reflect light imparting the shine to the products.
Developing right size and shape of pearly wax is a kind of complex technology (Norbert Boyxen in Olaz, Szappan, Kosmetica, 50 evofolyam (2001) and M. A. Bolzinger et al., Colloids and Surfaces A: Physiochem. Eng. Aspects, 93-100, 299 (2007) and getting the consistency in pearly sheen of the finished personal care products, batches after batches, is not always easy. This problem has been addressed by the ‘easy-to-use’ cold-dispersible pearlescent concentrates.
The surfactants manufacturing industry developed the technology to manufacture so called ‘cold-dispersible’, ‘free-flowing’ pearlescent concentrates for the ease of incorporation of pearly waxes into personal and home care formulations (U.S. Pat. Nos. 4,777,038, 4,824,594, 4,948,528 & 5,017,305). These ‘cold-dispersible pearlescent concentrates’ are nothing but pearl waxes dispersed in the crystal form in aqueous surfactant systems. These are very stable and concentrated, yet flowable, dispersions, that are required to be added anywhere between 0.5 to 5.0% to the personal or home care compositions to impart the pearlescent appearance. This operation is done with simple mixing without heating and hence these are referred to as ‘cold-dispersible’ (cold-processable) pearlescent concentrates. In addition to the benefits of ease of incorporation and saving of energy, the other significant advantage that is derived from these concentrates is that of the consistency in the pearlescent appearance in the final personal and home care compositions. Several cold pearlescent concentrates are available commercially, for example, Sparkle series from Galaxy Surfactants Ltd, Mirasheen series from Rhodia (Solvay), Euperlan PK series from Cognis (BASF), Zoharpearl series from Zohar Dalia and Quickpearl series from Lubrizol (Table I).
TABLE IManufacturerTrade nameIngredientsRhodia-SolvayMirasheen CP 920Ethylene glycol distearate,Laureth-7, Coamidopropylbetaine, Sodiumcocoamphoacetate, Sodiumlaureth sulfate, DMDMHydantoinRhodia-SolvayMirasheen STAR KEthylene glycol distearate Sodlaureth sulphate,Cocoamidopropyl betaineCognis-BASFEUPERLAN PK 1200Ethylene glycol distearateCoco-glucoside,Cognis-BASFEUPERLAN PK 4000Ethylene glycol distearate,Laureth-4, CocamidopropylbetaineCognis-BASFEUPERLAN PK 710Ethylene glycol distearateBENZSodium laureth sulfate,Cocamide MEA,Cognis-BASFEUPERLAN PK 710Ethylene glycol distearateSodium laureth sulfate,Cocamide MEACognis-BASFEUPERLAN PK 771Ethylene glycol distearate,Sodium laureth sulfate,Cocamide MEA, Laureth-10Cognis-BASFEUPERLAN PK 771Ethylene glycol distearate,BENZSodium laureth sulfate,Cocamide MEA, Laureth-10Cognis-BASFEUPERLAN PK 810Ethylene glycol distearate,Sodium laureth sulfate,Cocamide MEA, Laureth-10Cognis-BASFEUPERLAN PK 900PEG-3 stearate, Sodium laurethBENZ-WsulfateLubrizolQuickpearl ™ 810Ethylene glycol distearate,Sodium laureth sulfate,Cocamide MEA, Laureth-10LubrizolQuickpearl ™ IEthylene glycol distearate,Sodium lauryl sulfateLubrizolQuickpearl ™ IIEthylene glycol distearateSod laureth sulphateLubrizolQuickpearl ™ PK3Ethylene glycol distearate,Pearlizing AgentLaureth-4, CocamidopropylbetaineGalaxySparkle 660Ethylene glycol distearate,Surfactants LtdSodium laureth sulfate
Typically, all cold-dispersible pearlescent concentrates (TABLE I) are made of three components a) pearly waxes b) surfactants and c) water. Waxes are emulsified with surfactants in aqueous medium and then are gradually allowed to crystallize in the surfactant environment. This process results in a stable uniform dispersion of platelet like structures that reflect light. The examples of waxes are glycol esters of stearic acid or other fatty esters (Formula I) and alkanolamides (Formula H). The surfactants that are used to disperse the pearly waxes are from all categories, namely, anionic, cationic, amphoteric, zwitterionic and non-ionic (U.S. Pat. Nos. 5,560,873, 5,711,899, 6,147,124, & 7,578,995).
A quick look at commercial products and the patented literature reveals that the most commonly used ingredients for free-flowing cold-dispersible pearlescent concentrates are 1) ethylene glycol stearates 2) alkanolamides 3) sodium laureth sulphate (anionic surfactant) 4) cocoamido propyl betaine (zwitterionic surfactant) 5) ethylene oxide adducts of fatty alcohols (non-ionic surfactant) and preservatives (TABLE I).
Alkanolamides are synthesized by reacting fatty acids or their esters with monoethanol amine or diethanol amine to give corresponding alkyl monoethanolamides or alkyl diethanol amides. The alkanol amides, particularly, alkyl diethanol amides have been reported to generate carcinogenic nitrosoamines (U.S. Pat. No. 5,560,873) due to residual free diethanol amine. For example, cocodiethanol amide (Cocamide DEA) has significant amount of residual diethanol amine that can generate the carcinogenic nitrosoamine after coming in contact with other personal care ingredient that are capable of nitrosating the secondary amine. Cocamide DEA has been listed as cancer causing substance by the Office of Environmental Health Hazard Assessment of California state government, USA (California prop 65 list). Personal care formulators have become very wary of using Cocamide MEA (cocomonoethanol amide) since monoethanol amine used in the manufacture can have diethanol amine as an impurity since there is no way of synthesizing monoethanol amine exclusively and selectively without generation of diethanol amine.
Alkyl sulphates and alkyl ether sulphates are known for being harsh on both skin and hair. In fact sodium lauryl sulphate is taken as a standard irritant for irritancy measurement. Sodium lauryl ether sulphate (SLES) is made by sulphating ethoxylated lauryl alcohol of varying degree of ethylene oxide (0.5 to 3.0 moles of EO per one mole of fatty alcohol). Any grade of SLES that is available in the market contains significant amount of sodium lauryl sulphate (more than 20%) that is an established irritant to human skin and mucosa. In the class of anionic surfactants ‘sulphates’ in general are known to be the highest irritants compared to ‘sulphonates or sulphosuccinates’. While doing the cleansing job, alkyl ether sulphates strip away proteins and lipids of cuticle of hair and stratum corneum of skin. Skin's moisture regulation mechanism is seriously affected due to adverse action of harsh surfactants on the proteins and lipids of upper layers of stratum corneum. Products ‘without sulphates’ have been launched that do less or no damage to hair. An example of this is L'Oreal's ‘sulphate-free’ ‘Everpure’ range of shampoos. Unilever's Dove range of body washes uses mild surfactants like cocoyl isethionate and sodium glycinate to reduce damaging effect of harsh surfactants like fatty alchohol ether sulphates (Nutrium technology, A novel glycinate-based body wash, K. P. Ananthapadmanabhan et al., Journal of Clinical Aesthetic Dermatology 23-30, 6(6), 2013).
Ethylene glycol stearates, mono or di, are the main pearlizing waxes that are used in these concentrates and these are by far the largest active component in the cold-dispersible, free-flowing pearlescent concentrates that are either available commercially or reported in literature. This is because these are the substances that crystallize and impart pearly effect to the final composition. Ethylene glycol stearates are made by esterifying stearic/palmitic acids with ethylene glycol. Though fatty acids are largely obtained from vegetable oils, mainly palm and coconut oil, ethylene glycol (mono ethylene glycol, MEG) has its origin in a petrochemical, ethylene oxide. Besides MEG's petrochemical origin, the more worrisome fact is its toxicity. The major impurity, diethylene glycol (DEG) in MEG is a serious concern. Ethylene glycol is listed by American Association of Poison Control Center that keeps track of fatalities due to ethylene glycol. Ethylene glycol is a teratogen in animals and hence suspected to be teratogen in human being. (Hazardous Substance Fact Sheet on Ethylene Glycol, New Jersey Department of Health, USA. Monoethylene glycol is on the Special Health Hazard Substance List) This means it is a huge concern for the environment and the ecology. All personal care and home care products like body-washes and hand-washes go to environment after the usage and are biodegraded to give ethylene glycol from the corresponding pearly distearates. The impurity, diethylene glycol (DEG) in mono ethylene glycol is another poison. US code of federal regulations allow no more than 0.2% of DEG in polyethylene glycols used as food/drug or toothpaste additive. DEG is well-known poison and epidemiology is full of records of human deaths. In summary, in addition to being a petrochemical derived glycol, MEG is quite toxic due to impurities like DEG and by itself MEG is a danger to the environment due to its teratogenicity. There has been one commercial product by Cognis-BASF (Care chemicals division, Technical Data Sheet, EUPERLAN® GREEN) by the trade name Euperlan Green seems to be the only example wherein ethylene glycol stearate has been replaced by stearyl citrate and the non-ionic surfactant of lauryl glucoside is used to disperse the pearly wax. This was done with the intention of avoiding ethylene oxide (EO) based products.
Cocoamidopropyl betaine, CAPB is popular zwitterionic surfactant and very commonly used in pearlescent concentrates. It is manufactured from methyl ester of fatty acid or from fatty acids by reacting with N,N-dimethyl propyl diamine to get the corresponding amido amine that is subsequently quaternized by monochloroacetic acid into final zwitterionic surfactant. Though it is one of the most economical zwitterionic surfactant it is impossible to manufacture CAPB that would be totally devoid of traces of free N,N-dimethyl propyl diamine and monochloroacetic acid. Both starting materials that are used in the manufacture of CAPB are quite toxic (DIN safety data sheet on N,N-dimethyl propyl diamine, BASF, 1989). N,N-dimethyl propyl diamine is a skin-corrosive (Category 1B) and skin sensitizing (Category The other trace level impurity in CAPB is highly acidic and corrosive monochloro acetic acid, having LD50 76 mg/kg, which is reported to penetrate through skin and mucous membrane.
A survey of commercially available cold pearlescent concentrates reveals that use of parabens, formaldehyde releasers and isothiazolinones. To move away from the controversial substances some manufacturers adopted different strategy of maintaining the acidic pH and with acids as preservatives.
In some marketed pearly concentrates very acidic pH is maintained and the same are preserved with acids like benzoic acid or formic acid. For example Euperlan 771 is preserved with benzoic acid. Euperlan PK4000, Euperlan PK810 are preserved with formic acid. Similarly, MackPearl TTE and MacPearl SSO special are preserved with formic acid. Euperlan Green is preserved by maintaining very acidic pH of 3 to 4. Euperlan PK771 and Mirasheen Star K and Mirasheen Star NB are preserved with isothiazolinones. Mirasheen CP 820/G and Mirasheen A-220 are preserved with DMDM hydantoin.
It should be noted that these pearlescent concentrates are for personal care products and formic acid should not be used as preservative for end personal care formulation as it keeps the pH so acidic. Moreover, formic acid is corrosive to skin and is very reactive molecule and can react with a variety of functionality of other ingredients.
Methyl and chloro analogs of Isothiazolinone (commercial trade name Kathon CG by Rohm and Haas) are quite toxic and hence they are allowed at a few ppm levels and only in rinse-off products. They are not used in any leave-on products. Japan's regulatory body does not permit the usage of these Isothiazolinones analogs. DMDM hydantoin, another antimicrobial, prevalent in some of the pearlescent concentrates, is a well-known formaldehyde releaser.
In view of this prevalent use of these established toxic antimicrobials (parabens, isothiazolinones, formaldehyde releasers, halogenated compounds, phenolic molecules) it is very essential to preserve these pearlescent concentrates with something very effective but at the same time safe and eco-friendly.
U.S. Pat. No. 5,560,873 discloses pearlizing concentrates that address the above mentioned issues to some extent. It teaches use of mild surfactants like sodium cocoyl isethionate and sodium cocoyl N-methyl taurate in place of the harsh alkyl ether sulphates. The pearlescent blends of this patent are expected to be mild on skin since they do not contain fatty alcohol ether sulphates. However, this patent does not report or refer to any literature or include data to suggest any synergy in terms of mildness arising out of in any particular combination of O-acyl isethionate and N-acyl taurate.
It also teaches creating pearlescent concentrates without carcinogenic alkanolamides, which can be used in personal care compositions. However, the examples cited in this patent employ ethylene glycol monostearate as the pearly wax, and cocoamidopropyl betaine, zwitterionic surfactant. Also, the preservatives listed in this patent application are the most controversial antimicrobials, the parabens and the formaldehyde releasers like imidazolidinyl urea. Parabens have been reported to have endocrine disrupting estrogenic activity and some deleterious effect on reproductive system. Formaldehyde is classified as category 3 CMR (carcinogenic, mutagenic and reproductive toxic). Also, released formaldehyde is a very reactive chemical (aldehyde functionality) capable of reacting with several personal care ingredients.
Euperlan Green that obviates first four ingredients listed above, however, uses extreme acidity for the preservation purpose. This extreme acidity comes from significant level of free acid. Also, the constituent members of Euperlan Green have significant characteristic odor.
Personal cleansing compositions of today have undergone revolutionary change. Recently, Tsaur et al. have revolutionized cleansing technology by inventing various combinations of mild surfactants. Synergistic combinations of O-acyl isethionate and N-acyl glycinate/sarcosinate as ‘super mild’ surfactants are reported in the recent literature (U.S. Pat. Nos. 8,268,767, 8,263,538, 8,114,824).
U.S. Pat. No. 8,263,538 teaches a combination of N-acyl amino acid surfactants, such as sodium N-cocoyl glycinates and sodium N-cocoyl sarcosinates, with amphoteric/zwitterionic surfactants for ‘super mild’ personal cleansing compositions that showed total irritation score using patch test methodology to be less than 75% relative to 0.5% aqueous sodium dodecyl sulphate solution.
Yet another recent patent by the same group (Tsaur et al. U.S. Pat. No. 8,268,767) reports combinations of cleansing surfactants that not only cleanse, moisturize and deliver the benefit agents but are ‘super mild’ to skin. The said compositions comprise of both O-acyl isethionates (Formula III, R4=C7 to C21, R5=H, methyl and M is a cation selected from Na+, K+, NH4+) and N-acyl amino acid surfactants
(Formula IV, R4=C7 to C21, R5=H, methyl, M is a cation selected from NH4+, Na+ or K+) for liquid cleansers for both skin and hair.

The compositions are said to be ‘super-mild’ to skin when tested by standard patch test (in-vivo) method on human volunteers. The above mentioned patent also reveals exceptionally mild compositions that deliver the occlusive moisturizers very effectively. Similarly, U.S. Pat. No. 8,114,824 discloses compositions with O-acyl isethionates and N-acyl amino acid surfactants that could accommodate maximum amount of moisturizer. In summary, the surfactant systems comprising of O-acyl isethionates and N-acyl amino acid surfactants as main ingredients have been reported to be very good cleansing systems that are ‘super mild/gentle’ on skin and excellent delivery vehicles for actives (benefit agents like emollients, silicones, triglycerides and petrolatum). The above mentioned patent teaches that the ‘super mildness’ and ‘delivery benefits’ are obtained due to the exceptional synergy exhibited by the combination of these two classes of mild surfactants, namely, O-acyl isethionates (Formula III) and N-acyl amino acid surfactants (Formula IV).
The commercial products using the ‘super-mild’ surfactant combinations (K. P. Ananthapadmanabhan et al., Journal of Clinical Aesthetic Dermatology 23-30, 6(6), 2013) are being made (Dove body wash, Nutrium Moisture™ technology by Unilever, Fine Fairness Cleanser by Johnson and Johnson).
Today's consumer and the manufacturers of personal care products are conscious about the deleterious effects of chemicals that are used in formulations. Conscious efforts are being made to use the safest ingredients that are also eco-friendly and sustainable. Personal care formulators are formulating cleansing systems with ‘super-mild’ surfactants (for cleansing face, body and hair). Consciously, toxic ingredients are being avoided and this includes the anti-microbial preservatives. The adjectives like ‘sulphate-free’, ‘paraben free’ and ‘alkanolamide free’ are getting popular. Certainly, to improve the aesthetics of such carefully formulated products, the formulators need a cold-dispersible pearlizing concentrate that is not just made from safe and non-toxic substances but it should be completely eco-friendly and sustainable. Currently, no such cold-dispersible pearlizing concentrate is available.
Thus, there is need for a cold-dispersible pearlescent concentrate that would be devoid of all controversial substances including 1) harsh surfactants like alkyl sulphates/alkyl ether sulphates 2) alkanol amides based on monoethanol amine and diethanol amine 3) pearly waxes based on ethylene glycol 4) amidobetaines and 5) preservatives systems containing parabens, formaldehyde releasers, and isothiazolinones.